1. Field of the Invention
The present invention generally relates to a drive plate for vehicles, and particularly, it relates to a drive plate for vehicles of the type that includes an engine with a crankshaft and an automatic variable speed gear with a torque converter, in which the drive plate interconnects the crankshaft and the torque converter to each other.
2. Description of Relevant Art
Recent vehicles are mostly constituted such that a crankshaft has its tendency to turn (hereafter "turning effect" or "torque") transmitted to a wheel axle via a torque converter, as the torque is once transmitted to the torque converter from a drive plate fastened with the crankshaft.
FIGS. 1 and 2 show a conventional drive plate 1 for vehicles. The drive plate 1 comprises a body 2 formed from a metallic disk by a plastic working, and a ring gear 3 integrally joined to be fixed by a welding to an outer circumferential edge of the body 2.
The body 2 has a crankshaft fastening part 4 formed in a central portion thereof by a drawing, and a torque converter fastening part 5 in a radially outer peripheral portion. The crankshaft fastening part 4 is formed with a total of six crankshaft fastening holes 4a arranged on a circle in an equi-spaced manner (i.e. at a pitch); and the torque converter fastening part 5, with a total of three torque converter fastening holes 5a arranged on a circle in an equi-spaced manner. This fastening part 5 further has rigidity-controlling first additional openings 5b formed in respective vicinities of the fastening holes 5a, so that its rigidity or flexibility can be set for an adjustment by changing shapes of the additional openings 5b in a various manner. This is for permitting the fastening part 5 as well as an adjacent portion thereto to have a controlled rigidness for an adequate followability to axial deformations of an associated torque converter 7 which repeats an expansion and a contraction with a varying hydraulic pressure therein.
The drive plate 1 is fixed on the one hand to an end part 6a of a crankshaft 6 with fixing bolts 6b inserted through the crankshaft fastening holes 4a and on the other hand to boss parts 7a of the torque converter 7 with fixing bolts 7b inserted through the torque converter fastening holes 5a, thereby for transmitting torque of the crankshaft 6 to the torque converter 7 and for absorbing positional variations of fixing points due to the expansion and the contraction of the torque converter 7.
The torque converter 7 deforming with a repeated expansion or contraction due to an internal hydraulic pressure has a thrust deformation. If the drive plate 1 was too rigid in an axial direction thereof, the torque converter's thrust deformation would affect the crankshaft fastening part 4 in a directly acting manner, imposing a great thrust load on a thrust bearing of the crankshaft 6. The thrust bearing might then be broken or damaged. To this point, the additional openings 5b effectively serve for absorbing the thrust deformation, with a moderate load, preventing larger thrust loads from being transmitted to the crankshaft 6.
To render the transmittable thrust load more moderate, there has been proposed a drive plate shown in FIG. 3. This conventional drive plate 1 has formed in a crankshaft fastening part 4 thereof a plurality of rigidity-controlling second additional openings 4b (six in total in the figure) arranged in an equi-spaced manner on a circle outside the crankshaft fastening holes 4a, for providing the fastening part 4 with an increased flexibility, so that a thrust load due to a deformation of a torque converter is additionally reduced to be transmitted to a crankshaft.
In the drive plate 1 of FIG. 3, however, the second additional openings 4b are all equi-spaced along a circle, by providing an interconnection region between a respective pair of circumferentially neighboring ones of the first additional openings 5b with a higher rigidity than vicinal regions of these additional openings 5b. On the other hand, as the drive plate 1 rotates, it has torsional moments acting thereon, generating stresses therein. Therefore, when the plate 1 is rotated, such stresses are concentrated on those vicinal regions of the first additional openings 5b that are designated by reference character A in FIG. 3, resulting in a tendency to provide the torque converter fastening part 5 with a reduced torsional strength.